Zinc-base die-casting alloy



Patented Apr. 5, 1932 UNITED STATES PATENT OFFICE mmunn A. ANDERSON AND arouse L. WEBLEY, or summon, rmmsynvama,

ASSIGNORS TO THE NEW JERSEY ZINC COMPANY, OF NEW IPOBATION OF NEW JERSEY ZINC-BASE DIE-CASTING- ALLOY Illo Drawing.

This invention relates to zinc base die-casting alloys and has for its object the provision of unimproved alloy of this character.

The mechanical requirements of the die-' a casting operation necessitate the construction t to the zinc, in order to minimize this attack suficiently to secure reasonable life from the apparatus. Alloys for die-casting must possess a sufl'icient degree of fluidity to pro erly flow into and completely fill the dies use l and 2% or more aluminum appears to be necessary to secure an adequate degree of fluidity.

It has also long been known that aluminum' increases the tensile strength of zinc and this, in itself, makes its presence in zinc base diecasting alloys desirable in quantitiesof from 2% to as much as to Zinc-aluminum alloys containing less than about 80% of aluminum undergo a structural change subsequent to solidification which is commonly known as a phase change or more specifically in this case as an eutectoid reaction. This phase change consists in the formation of two crystalline forms or phases from one phase previously existing, and is accompanied by certain changes in physical properties of the alloy, such, for example, as increase in density, hardness and tensile strength and decrease in ductility and impact 1;, strength. This phase change may occur during the cooling of the alloy after casting or may through certain influences be retarded or inhibited. In such cases it may take place gradually over a period of months at ordinary temperatures.

A secondary stage of phase change which sometimes occurs is the growth of coalescence of the extremely small particles of the new phases as first formed into larger particles. This stage may be accompanied by softening YORK,- N. Y A 00B- Applicationfiled Anut 19, 1930. Serial No. 478,452.

and lowering of tensile strength and by an increase in ductility and impactstrength.

Zinc-aluminum alloys in this range of composition are also subject to a type of disintegratio'n commonly known as 'intercrystalline oxidation. In extreme cases, under the influence of warmth and moisture, intercrystalline oxidation may completely penetrate specimens of these alloys and cause I swelling, Warping and even complete disintegration. Intercrystalline oxidation is in some way associated with and partly dependent upon the phase change.

It has heretofore been recognized that certain other metals when present in these zincaluminum alloys exercise important efi'ects on either the phase change or the intercrystalline oxidation or both. For example, cop

per and magnesium are known to exert an influence on the phase change either in respect to the rate at which it takes place or the completeness of the reaction or in some otherrespect not fully understood. The particular effect produced by copper and magnesium on the phase change reacts favorably in increasing the resistance of the alloys to intercrystalline oxidation. Lead, while not exerting any marked influence on the phase change, very seriously diminishes the resistance of these zinc-aluminum alloys to intercrystalline oxidation. Cadmium, though having a certain effect on the phase change, in the presence of lead usually diminishes the resistance of these alloys to intercrystalline oxidation.

Zinc base alloys suitable for die-casting are known and in use. An alloy containing 4% aluminum, 3% copperfand the balance high grade zinc metal is widely used and is satisfactory for many purposes. This alloy is, however, open to two objections: First, upon aging, either at normal temperatures or at presence of warmth and moisture together,

the alloy undergoes intercrystalline oxidation namely, loss of impact strength and change of dimensions upon aginlg. This objectionable property of these a oys prevents their use in a wide field of otherwise suitable applications. These alloys have a. very high tensile strength much beyond that ordinarily needed and the elimination of the faults just described even at the expense of a considerable reduction in tensile strength is advantageous. This patent prescribes the well known Horsehead brand zinc metal, which averages 99.94% and contains about 0.045%.

lead'and about 0.003% cadmium. As is pointed out in the copending application below referred to, even impurities of these minute amounts exert extremely deleterious influ' ences on the ultimate physical properties of the alloys.

In copending application Serial No. 368,7

of Edmund A. Anderson, filed June 5, 1929, (which has since issued into United States Patent No. 1,779,525 of October 28, 1930), there is disclosed an alloy in which this objectionable property of loss of impactstrength and change of dimensions on aging is substantially eliminated, though at the expense of tensile strength. In the preferred composition of this copending application, the alloy contains 4% aluminum, .1% magnesium, and the zinc base is zinc metal of high purity, containing not more than .01% lead plus ca 'um.

It is an object of the present invention to improve the tensile strength after aging of zinc-base alloys, such as those described in the copending application above referred to, while substantially retaining certain ad vantages claimed for the said alloys. It is pointed out in copending application Serial 1&0. 368,730 that the loss of impact strength and change in dimensions which'occur on aging in the well-known alloys containing 4% of aluminum and 3% of copper, with or without other additions, are related to the presence of copper.

We have found by further investigations,

however, that the presence of copper in limited amounts in the alloys of the copending application results in an improvement in tensile strength after aging without serious detriment to certain desirable properties claimed for the said alloys.

Based on these discoveries, our present mvention resides in the provision of an improved zinc base die-casting alloy containing an appropriate amount of aluminum for diecasting purposes, say, 2 to 10% (preferably about 4%), from 0.01 to 0.3% magnesium (preferably about 0.1%) copper in amounts up to 2% (preferably about 1%), and the balance high grade zinc metal (preferably containing more than 99.94% zinc).

More particularly, the invention involves the revision of an improved zinc base diecasting alloy containing from 2 to 10% of aluminum, preferably not more than 5%, from 0.01 to 0.3% magnesium, 0.05 to 2% copper, and in which the zinc base is zinc metal of high purity containing not more than 0.01% of'lead plus cadmium and not more than 0.001% tin.

In addition, the invention contemplates the provision of a die-casting made of a zinc base alloy and characterized by an impact strength that is not substantially impaired or (le- QO creased upon aging at normal or slightly elevated temperatures, and further characterized by a substantially negligible change in linear dimensions upon aging, and by an improved tensile strength after aging. It has heretofore been recognized that superior results are usually obtamed by employing high grade zinc metal as the zinc base in the known die-casting alloys. The well-known Horsehead brand zinc metal has been considered eminently satisfactory for the purpose, and it has not been considered necessary or advantageous to use zinc 'metal of higher purity. The I-Iorsehead brand zinc metal averages 99.94% zinc and contains about 0.045% lead and about 0.003%

cadmium.

In its preferred form, the improved zinc base die-casting alloy of the invention is made of a zinc metal base ofhigh purity containing not more than 0.01% leadplus cadmium. Preferably, the zinc base alloy of the invention contains about 4% aluminum, about 0.1% magnesium, about 1% copper, and the balance zinc metal of high purity containing not more than .01% lead plus cadmium. Tin should be substantially excluded from the alloy, and in no case should TABLE I C'omposition of alloy.

Zinc metal containing- Alloy Al Cu Mg Pb Cd TABLE II tensile specimens Alter exposure to steam at 95 C. Aft r 30 days Alloy As cast i exposure 1 day days days days g $82 5; I 43, 300 4'3. 000 38, 600 42,100 33, 600 31, 900 29. 400 1 33,000 31, 200 30,000 33, 000 34, 100 32, 700 32, 500 35, l 35, 700 33, 400 33, 900 37, 400 37, 400 30, 400 36, 200 37, 300 l TABLE III Impact strength in foot pounds per sq. in.

After exposure to steam at 95 C. Aft r days Alloy As cast exposure 1 day 5 days 10 days 20 days a: 257. 6

TABLE IV Linear ewpa nsion in inches After exposure to steam at 95 C.

30 days Alloy 3,5 exposure 1 day 5 days 10 days 20 days g: ga

. 7431 0005 (D05 0019 (D19 .7427 0001 0003 0009 (1)13 0!!)7 .7431 0002 .(D01 .0001 .(DM [D02 7432 -.0003 .0000 .0003 .(IDQ -.(XX)5 .7436 -.0001 --.0(I)1 .0006 .0007 -.0002 .7434 .0000 .0001 .0117 A1119 .011)! As will be seen from the foregoing tables,

the improved alloy of the invention, in its preferred form, exhibits materially greater tensile strength, both in its original condition and after aging, than the preferred composition of copending application Serial No. 368,730, and at the same time exhibits a similar unusual retention of dimensions and other physical properties after accelerated aging. This permits the use of die-castings made of this alloy where a high permanent tensile strength is necessary in addition to freedom from objectionable impairment of 1. A zinc base alloy consisting of 2 to 10% aluminum, 0.01 to 0.3% magnesium, 0.05 to 2.0% copper, and the balance zinc.

2. A zinc base alloy consisting of approximately 4% aluminum, 0.1% magnesium, 1.0% copper, and the balance high grade ZlIlC.

3. A zinc base alloy consisting of 2 to 5% aluminum, 0.01 to 0.3% magnesium, 0.05 to 2.0% copper, and the balance zinc metal containing 99.99% or more zinc.

4. A z inc base alloy consisting of from 2 to 10%aluminum, from 0.01 to 0.3% magnesium, from 0.05 to 2.0% copper, and in which the zinc base is zinc metal containing 99.99% zinc and less than 0.01% of lead plus cadmium.

5. A zinc base alloy consisting of about 1% aluminum, about 0.1% magnesium, about 1.0% copper and in which the zinc base is zinc metal of high purity containing not more than 0.01% of lead plus cadmium.

In testimony whereof we aflix our signa- 

